Atrial fibrillation (AF) is characterized by the irregular and very rapid beating of the heart's atrial chambers and results when the normal electrical conduction system of the atria malfunctions, leading to irregular and chaotic electrical signals. During AF, the regular pumping action of the atria is replaced by irregular, disorganized and quivering spasms of atrial tissue. These spasms may lead to reduced blood flow, blood clots, stroke and even death. This malfunction results in the failure of the atria to fill the ventricles completely and, consequently, the failure of the heart to pump adequate amounts of blood to the body. Once AF becomes symptomatic, it is typically associated with significant morbidity related to reduced blood flow. Often, the greatest concern is that the reduced cardiac output can lead to blood pooling in the atria and the formation of blood clots. Blood clots in the left atrium can dislodge and travel through the bloodstream to the brain, resulting in stroke and even death.
In the United States, AF currently affects an estimated two million people, with approximately 160,000 new cases being diagnosed each year. About 1.5 million outpatient visits and more than 200,000 patient admissions per year in the United States are associated with AF. AF is responsible for over 70,000 strokes each year in the United States alone; the annual cost of treating these patients is more than $3.6 billion. The cost of drug treatment for AF alone is estimated to be in excess of $400 million worldwide each year.
Current AF treatments are directed to reestablishing a normal heartbeat and preventing stroke, and are primarily supportive and palliative rather than curative. Antiarrhythmic and anticoagulant drugs (such as sodium and calcium channel blockers) or drugs which reduce the Beta-adrenergic activity are the most common treatment for AF. These drugs are used to control AF by restoring the heart's natural rhythm and limiting the natural clotting mechanism of the blood. However, antiarrhythmic drug therapy often becomes less effective over time, with approximately half of the patients eventually developing resistance. In addition, antiarrhythmic drugs can have severe side effects, including pulmonary fibrosis and impaired liver function.
Another palliative procedure for AF is external cardioversion, or the application of strong electrical current under general anesthesia. This treatment is usually only effective for a limited period of time as well. Implantable atrial defibrillators are being investigated to detect the onset of AF internally and then deliver an electrical shock to convert the heart back to normal rhythm. Although the preliminary results of clinical studies indicate that this approach may be feasible, AF is not cured with this approach. There are also significant problems with this treatment, including pain tolerance, reversion to AF and creation of ventricular tachycardia as a result of the electrical shock.
Purposeful destruction of the Atrio-Ventricular (AV) node followed by implantation of a pacemaker is typically a treatment of last resort for AF patients, but does not cure or treat the AF itself Since atrial function remains poor following the procedure, chronic anticoagulant therapy is generally required.
Another therapy for AF is an open heart operation. In a technique known as the "maze" procedure, a surgeon makes several slices through the wall of the atrium with a scalpel and then sews the cuts back together, creating a scar pattern. The scars isolate and contain the chaotic electrical impulses to control and channel the electrical signal emanating from the SA node.
This open heart operation is expensive and associated with long hospital stays, high morbidity and mortality. Although this approach is not commonly used because it is highly invasive, containing the movement of the chaotic impulses in the atrium through scar creation is generally considered effective in controlling AF.
An alternative to open heart or open chest surgery is a minimally invasive treatment technique in which radiofrequency (RF) ablation catheters are used to form thin, continuous linear scars in various locations in the atria. This procedure has the promise of safely treating AF with significantly reduced trauma.
Although such RF ablation catheters have proliferated in recent years, the technique is still in its infancy. Difficulties associated with clearly imaging and accessing various portions of the cardiac anatomy to create the desired lesions exemplify some of the shortcomings of this treatment that still have yet to be overcome.
One treatment combines the advantages of the open heart "maze" procedure and RF catheter-based treatment such that lesions are created in an open heart environment with one or more RF electrodes and not the surgeon's scalpel. However, there is a significant unresolved need to provide a tool adequate to perform such a procedure in a safe, effective, and reliable manner.
What is needed is an ablation device which can be used as a surgical tool that assures adequate tissue contact prior to ablation but which is flexible enough to create both straight and curved lines of conduction block, etc. in endocardial and epicardial applications.